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MG MGA - Engine noise diagnosis
|Starting to be concerned about a background engine noise on my 1622 that is puzzling me. The noise has been round for a while but is starting to be more pronounced. Here are the symptoms.|
Sounds like a pronounced tappet noise but I have double checked the tappet clearances. The noise is not a 'chatter' but a single tappet like noise.
Have disconnected the fan belt and no change.
Noise gets faster with engine revs but is unaffected by engine load.
Seems to come from the top end within the rocker cover but difficult to isolate and could be coming from elsewhere
Oil pressure and engine performance is good.
Any suggestions will be much appreciated.
|J H Cole|
|If you can get an engine stethoscope, use it to narrow down the noise location, they can be quite accurate. You can also try a long blade screw driver with the handle placed on the ear. Just don't put the blade on anything that is moving!|
|Hi, When was the last time you changed your clutch release bearing? A few years ago, I had a rhythmical "knock" that was tied to engine speed. After lots of fruitless diagnosis, I pulled the engine to do a physical examination. When the transmission was removed, I found that the carbon block on the release bearing was worn right down to the casting!. When the clutch pressure plate rotated, it hit a high spot on the release bearing, which caused a rhythmic tick that varied with engine speed. Noise went away as soon as I installed a new release bearing. Perhaps you have a different issue, but if all else fails in diagnosis you might want to keep this in mind. Cheers, Glenn|
|Could be a cam follower (lifter). Clearances would be OK.|
Or a leaking exhaust gasket.
|A worn rocker shaft was the culprit on my 1500, worth a look before you pull the engine out!|
|Do what I do with my not dissimilar noise - turn the radio volume up.|
|Take off the rocker cover. With the engine running slide an old feeler gauge or piece of shim of about 5 thou between rocker and valve stem. |
If the noise goes away you have isolated it down to one valve. You could then either try to find what is wrong or adjust the noise out.
Now clean up the oil drops from the wings, the engine and yourself.
|Thanks for all the suggestions.|
GG I think its from the top end, I've tried the listening through a pipe approach but can't get close to the source. GH My gut feeling is the top but I know that sound can track and be misleading, engine has done about 12,000 miles. AP I've recently put new MGB followers in but some of the old MGA followers were pretty bad (as Barneys pics). LS I think the rocker shaft is not too bad. SG I know what you mean, I've been ignoring it for a while but now its irritating me. I make a point of listening out for the tapping every time I drive (sad). Mine's a coupe and you get a lot of engine noise into the cabin. MA will try your suggestion and see if I can get closer to the source.
Here are my worst fears:
one or more camshaft lobes badly worn.( but still can't see why I can't adjust it out).
One valve hitting the block.
I recently fitted a Austin 1800 head that required eyebrows. All done as per Barney but suppose one eyebrow is still too shallow and the valve is just touching the block. (Am I right in thinking that if I slacken off the tappet clearances -say a lot-one by one, this will reduce the valve drop and might eliminate the noise thereby identifying the source?
|J H Cole|
|On a rebuild amongst everything else, I replaced the camshaft, camshaft bearings and cam followers and it still tapped. I nailed it down to No.2 tappet with a feeler gauge while running, I also noticed oil really flooding out of that No.2 rocker bearing. Engine stopped - I found that rocker twisted sideways, whereas the rest really didn't move much. So that bearing was shot. I replaced the whole rocker shaft assy - that did it... An MGA with quiet tappets!|
|You can check the camshaft with a dial indicator. Measure the rocker arm displacement directly over the pushrod, or at the valve end with a correction in the displacement due to rocker arm ratio. I don't have the numbers handy at the moment but all are available in the manual.|
|Thanks GG, I've checked the manual but can't find details of the camshaft lift. Can you point me in the right direction?|
|J H Cole|
|Pete, that sounds exactly like what I found on my rockers; oil flooded out of the worn ones. I just replaced the shaft and two of the rockers and the noise was gone, and with the engine running, oil just oozed from the rocker bearings. I discovered, on a later complete engine strip, that the camshaft was completely shot, but that wasn't causing any tapping noises at all!|
|JH have you fitted a later MGB type timing cover. If so, did you use the MGA oil thrower? If you did it's the wrong type and will be rubbing against the inside of the timing cover. Mine finally disintergrated and made the loud tapping noise that sounded just like a tappet out of adjustment.|
|AP its been about 8 years since I did the engine and the only change I made was to fit the newer neoprene oil seal. GG I found the cam lift info on Barney's site - I believe its 0.355 inch. I will try and rig up my digital vernier gauge over each rocker and indirectly check the cam lobes.|
|J H Cole|
|JH, you are right, the cam lift specs are not in the manual (I had to look at my manual to refresh my memory). Use the Valve Lift spec and divide that by the Rocker Ratio to get the cam lift. For a 1500 motor, that's .357 divided by 1.426 for a cam lift of .250 inch. I've confirmed that number with a cam lift chart I have from University Motors Ltd. The lift is the same for both intake and exhaust. You can use the same method to confirm Barney's number if you wish.|
Good Luck, George
|Managed to measure the cam lift by bolting on a small steel section over the rocker pillar studs to use as a reference point and measured the cam lift with a vernier. 3 results were dead on 0.25 inch with the rest at 0.25 -0.005 inch. The method of measuring was not as good as a dial gauge but I'm left with the feeling that the cam is not too bad. BUT using MA's suggestion I measured the tappet clearances with the engine running and when I reached valve number 7 the noise suddenly stopped with the feeler gauge inserted. I'm still puzzled because I've checked all of the tappets 2 or 3 times and I know their at 0.015 or a tad less. Why this valve with the correct clearance should be making such a noise compared with the others I'm not sure but I've wound it down to 0.013 and the noise has all but gone away. -An almost quiet engine. Thanks for all of the suggestions.|
|J H Cole|
|Check the contact area of your rocker. It may have a worn groove that you cannot adjust stactic clearance because your feeler gauge bridges the area and gives you a totally false reading. The solution is to have the rockers refaced or replaced.|
|I've been there J H, check your rocker shaft!!|
|I was checking my tappets for years trying to shut them up and of course the clearances were correct, so why would one have been noisey? Have you run it with the cover off yet to look for gushing oil from your No.7? Have you tried twisting the rocker sideways to see what movement there is compared to the others?|
|I would LS but I don't want to undo all the head studs. I get really nervous putting 50 ft-lb torque onto my 50 year old studs. Is it the generally accepted view that you can safely undo the studs holding the the rocker shaft only and leave the others fully torqued? PT -yes I found the noisy tappet by inserting a gauge whilst the engine was running. I've tried twisting the rockers and they all move a little, much the same as does the oil seeping out of the bearings although some are worse than others. I don't get anything that approaches a gush. If the noise starts up again I will as LS says have the shaft out and inspect it together with the rockers. Thanks to all.|
|J H Cole|
|J H, your 50 year old studs are probably less likely to break than their modern replacements. I've still got the original studs on my engine and have slackened and re-tightened four times without a breakage so far.|
The oil seaps very slowly with the new rocker shaft, you have to watch the shaft bearings for several seconds to see the oil movement. With the old shaft, the oil flow was very obvious. I also found that I could lessen the tapping noise by reducing the valve clearances, but was not happy about running the engine that way. I think worn rocker shafts are quite common. What often happens is that the shaft oil way gets sludge in it, thus compromising the oil flow to some of the rockers, usually those furthest from the oil feed end of the shaft, so in that case you may find less oil flow on the worn ones because they are running "dry".
This thread was discussed between 07/04/2010 and 11/04/2010
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